Engineers are constantly seeking ways to reduce undesirable engine emissions. One strategy is to seek ways to improve performance of fuel injection systems. Over the years, engineers have come to learn that engine emissions can be a significant function of injection timing, the number of injections, injection quantities and rate shapes. A fuel injection system with a variety of capabilities to produce a variety of injection strategies can better perform and reduce emissions at all engine operating conditions than a fuel injection system limited in its control over injection timing, number, quantity and rate shapes. Further, increases in the ability to vary injection rates, injection numbers, injection quantities and rate shapes can lead to more research on, and discovery of, improved injection strategies at different operating conditions.
One apparent attempt to provide a fuel injection system that can quickly vary the pressure of injections is disclosed in U.S. Pat. No. 6,453,875 B1, issued to Mahr et. al. on Sep. 24, 2002. The Mahr fuel injection system includes a common rail and a directly controlled fuel injector that has the ability to inject medium pressure fuel directly from the rail, or utilize the fuel common rail to pressure intensify fuel within the injectors for injection at relatively high pressures. Fuel can flow from the common rail to the fuel injector via a pressure line. The fuel can either flow through a valve to act upon the pressure intensifier to inject at an intensified pressure, or bypass the valve, and be injected into an engine cylinder at rail pressure. The valve controlling the flow of fuel to the pressure intensifier is incorporated within the pressure intensifier, which may or may not be included in the fuel injector itself.
Although the Mahr fuel injection system can vary the pressure of injections, the fuel injector can consume valuable space adjacent and within a cylinder head. Because the fuel being directly injected in the cylinder and the fuel actuating the pressure intensifier flow from the same source, i.e, the fuel common rail, the fuel acting on the pressure intensifier is at rail pressure, which is generally greater than the pressure of other hydraulic fluid, such as oil, that can be used to actuator the pressure intensifier. For instance, the pressure of the fuel can be three to four times greater than the pressure of oil in an oil-actuated pressure intensifier. Thus, the fuel-actuated fuel injectors, such as the Mahr fuel injector, must be sufficiently sized and sealed in order to withstand the high fuel pressure. Because there is a limited spatial envelope around and within the cylinder head for the fuel injector, the design and capabilities of the fuel-actuated fuel injector may be limited by spacial constraints. In other words, some engine systems simply do not have a spacial envelope that can accommodate the fuel-over-fuel intensified system of the type described in Mahr.
The present disclosure is directed at overcoming one of more of the problems set forth above.